4.3.4 DATA FLOWS AND TRANSFORMATIONS IN THE ACCESS FUNCTIONAL AREA
When a Consumer wishes to use the data within the OAIS, a Finding Aid may be used to locate information of interest. Finding Aids present Consumers with the logical view of the OAIS holdings so the Consumers can decide which AIPs to acquire. At a minimum, the access view is the high-level logical view of the Collection Descriptions discussed in 18.104.22.168. The OAIS may have to spend significant time and effort developing Associated Descriptions and Finding Aids such as catalogs that will aid the Consumer in locating AIPs or AICs of interest. A Consumer will establish a Search Session with the Access entity. During this Search Session, the Consumer will use the OAIS Finding Aids to identify and investigate potential holdings of interest. This searching process tends to be iterative, first identifying broad criteria and then refining the criteria on the basis of previous search results. When candidate objects of interest are identified, more sophisticated Finding Aids such as browse image viewers or animation may be used to further refine a Result Set.
Once the Consumer identifies the OAIS holdings to acquire, the Consumer uses an OAIS- supplied Ordering Aid to develop an order request to acquire the data. The Consumer produces a logical view of the desired AIPs and associated Package Descriptions to be included in the Dissemination Information Package and specifies the physical details of the Data Dissemination Session such as media type and object format. This process may involve no visible interaction between the Consumer and the OAIS if adequate defaults exist. The order can also specify any transformations the Consumer wishes applied to the AIPs in creating the DIP.
The Access functional area then records the Order Agreement in the Data Management functional area. When the conditions required to satisfy a recorded Order Agreement are met (for many Order Agreements these conditions are met immediately, but if not Administration notifies Access when they are met) the Access functional area coordinates the response. Access contacts the Storage and Data Management functional areas and requests the AIPs and associated Package Descriptions necessary to populate the DIP requested by the Consumer. The Storage and Data Management functional areas create copies of the requested objects in temporary storage.
Access then transforms this set of the AIPs and associated Package Descriptions into a set of DIPs and stores those DIPs onto physical distribution (either physical or communications) media to be delivered to the Consumer in a Data Dissemination Session. The complexity of this transformation process can differ greatly on the basis of the level of processing services offered by the OAIS and requested by the Consumer’s order. In the simplest case, the DIP contains duplicates of the AIPs and associated Package Descriptions of interest from Storage and Data Management function. In more complex cases, the desired Content Information may have to be extracted from the information objects or inserted into self-describing information objects, and the encoding of the information objects or their allocation to physical files may have to be changed. In the most extreme case, when the OAIS supports subsetting services, the granularity of the information objects may be changed, and the Dissemination process may generate DIPs and associated Package Descriptions reflecting the new granularity. The mapping between DIPs and AIPs is one-to-one if no transformations are requested; however, the use of subsetting services and other product processing options could create many DIPs from a single AIP, or a single DIP based on combining many AIPs.